Development of red blood cell autoantibodies following treatment with checkpoint inhibitors: a new class of anti-neoplastic, immunotherapeutic agents associated with immune dysregulation.

Ipilimumab, nivolumab, and pembrolizumab represent a new class of immunotherapeutic drugs for treating patients with advanced cancer. Known as checkpoint inhibitors, these drugs act to upregulate the cellular and humoral immune response to tumor antigens by inhibiting T-cell autoregulation. As a consequence, they can be associated with immune-related adverse events (irAEs) due to loss of self-tolerance, including rare cases of immune-related cytopenias. We performed a retrospective clinical chart review, including serologic, hematology, and chemistry laboratory results, of two patients who developed red blood cell (RBC) autoantibodies during treatment with a checkpoint inhibitor. Serologic testing of blood samples from these patients during induction therapy with ipilimumab and nivolumab, respectively, showed their RBCs to be positive by the direct antiglobulin test (IgG+, C3+) and their plasma to contain panreactive RBC autoantibodies. Neither patient had evidence of hemolysis. Both patients developed an additional irAE during treatment. A literature review for patients who had developed immune-mediated cytopenia following treatment with a checkpoint inhibitor was performed. Nine other patients were reported with a hematologic irAE, including six with anemia attributable to autoimmune anemia, aplastic anemia, or pure RBC aplasia. Hematologic irAEs tend to occur early during induction therapy, often coincident with irAEs of other organs. In conclusion, checkpoint inhibitors can be associated with the development of autoantibodies, immune-mediated cytopenias, pure RBC aplasia, and aplastic anemia. Immunohematology reference laboratories should be aware of these agents when evaluating patients with advanced cancer and new-onset autoantibodies, anemia, and other cytopenias.